Integration of Simulations and Experiments for Modeling Superalloy Grain Growth

Grain size is an important parameter controlling the mechanical behavior and useful life of turbine disks. During heat treatment above the gamma prime (γ′) solvus the grain size increases dramatically as the γ′ particles dissolve. The grain size then stagnates as the volume fraction of the γ′ phase approaches zero. In general, the grain size at stagnation cannot be described by classic Zener pinning theory because of its strong dependence on the strain rate and thermal exposure during thermomechanical processing. The grain size distribution, twin boundary fraction, γ′ size distribution and volume fraction, carbide size distribution and volume fraction, γ′ dissolution rates, and carbide coarsening rates have been measured in two powder metallurgical disk superalloys. Stored energy and boundary properties after deformation have been assessed. The experimental results have been used as input parameters for a physics-based model of grain growth in a field of two populations of particles, one coarsening and one dissolving. Phase field models have been used to support and clarify interpretations of experimental results and to validate the appropriate functional forms for precipitate coarsening and dissolution. Comparison of experimental and modeling results have suggested avenues for further experimental investigations and vice versa. This established feedback loop between experimentation and simulation has enabled focused experimentation, increasing the accuracy and general applicability of the model.